Federal health officials said Monday that an implantable drug pump that Medtronic Inc. recalled this year had a potentially life-threatening design problem. The pump, called the SynchroMed II, delivers drugs directly into the spinal fluid to treat chronic pain and spasticity. The problem relates to the formation of a film within the pump's battery that could hurt the battery's performance and stop the therapy. Fridley-based Medtronic recalled the product in July, notifying the Food and Drug Administration, patients and doctors about the issue. At the time, the problem had arisen in 55 cases, including one death due to drug withdrawal, among 139,653 SynchroMed II pump implants worldwide.